Effect of heat treatment on green machinability of SiAlON compacts

• A simple heat treatment is used to improve green machinability of SiAlON compacts.
• Formation of the eutectic liquid plays a critical role on the green machinability.
• Before formation of the eutectic liquid, tool wear increases gradually.
• The chip shape changes as a result of eutectic liquid formation.

SiAlON based ceramics are promising materials for wear applications such as wire extrusion dies, pipe bending rollers, etc. due to their outstanding mechanical properties both at high and low temperatures. To be able to utilize these materials for such applications, they should have specific geometrical details as holes, threads, groves, etc. for the ease of fixation. Machining of a ceramic component in its green state is one of the most common techniques which enable producing SiAlON wear parts with desired geometries. It is a prerequisite for green machining that the compact should have a sufficient green strength to withstand against stresses at the cutting zone during machining. In this study, the required green strength was obtained by a simple heat treatment step performed between 1100 and 1400 °C. The effect of this process on the microstructure, phase development, strength and machinability of SiAlON green compacts were investigated. It was observed that the compacts heat treated at 1400 °C provide a sufficient strength against damage formation on the machined part and a relatively low tool wear as a result of the formation of fragmented chips during the cutting process. Although these fragmented chips have beneficial effects on the tool wear, they resulted in a relatively poor surface quality in the machined parts.